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Dose this unit have the carbon as the last stage ? If it dose (common on units sold for household use) and it's a new carbon cartridge, the TDS reading might be from some of the fine carbon particles

Have you tried testing the water as it comes out of the unit ?

Have you tried backflushing the system to get some of the TDS particles out of the membrane ?

I personally would not use water with 300 TDS. Could your TDS meter be giving you wrong readings ?

Last edited by Cliff; 01-09-2013 at 12:47 AM.

If you take your time to do the research FIRST, you can successfully set-up and keep ANY type of aquarium with ease."Not using a quarantine tank is like playing Russian roulette. Nobody wins the game, some people just get to play longer than others." - Anthony CalfoFishless CycleCycling with FishMarine Aquarium Info [URL="http://saltwater.aquaticcommunity.com/"]

If your water is pretty dirty I guess it could get need changing already. 275 gals is a lot.
\if you don't backflush every 50gals or so it would get dirty faster.

I wouldn't use it either, except as my first fill/cycling tank...2-4 tds is a sign that the filter needs maintenance...tho people do use water with higher tds than that. I did use straight tap water for my very first fill.

As Cliff asked, what is the TDS of the RO/DI water as it exits the unit?

If possible, are you also able to measure the RO water as well? (the water exiting the RO membrane prior to it entering the DI stage).

The TDS of the tap water in my area is currently about half that of your's (low to high 200s), but I've made hundreds of gallons of water since I last changed my membrane and filter stages and the TDS of the RO water is 1ppm (RO/DI output is 0ppm).

I think in a high TDS environment the DI resin may become depleted fairly quick (some hundreds of gallons) but the RO membrane should last quite a while. I've gone years between RO membrane change outs. How long has the RO membrane been used?

To cover all bases, could the the tank that is being filled have any TDS source (is it a used tank or brand new tank?), and is it completely empty (or does it contain any substrate or rocks?).

As Cliff asked, what is the TDS of the RO/DI water as it exits the unit?

If possible, are you also able to measure the RO water as well? (the water exiting the RO membrane prior to it entering the DI stage).

The TDS of the tap water in my area is currently about half that of your's (low to high 200s), but I've made hundreds of gallons of water since I last changed my membrane and filter stages and the TDS of the RO water is 1ppm (RO/DI output is 0ppm).

I think in a high TDS environment the DI resin may become depleted fairly quick (some hundreds of gallons) but the RO membrane should last quite a while. I've gone years between RO membrane change outs. How long has the RO membrane been used?

To cover all bases, could the the tank that is being filled have any TDS source (is it a used tank or brand new tank?), and is it completely empty (or does it contain any substrate or rocks?).

I may be able to measure the R/O. I will have to check tonight

The membrane was replaced few months back. The filter was only being used for top off on the tanks during that time.

It is possible that some salt mix is still in the tank along with some sand causing higher TDS. The tank has nothing else in it.

I bought new RO membrane, DI media, Carbon filter, 1 micron filter and an extra chamber for an extra carbon.

I have very high chlorine.. somethings enought to smell like you went swimming in a pool after a shower. Was told that once the carbon is used up by the chlorine it can burn up the rest of the chambers which caused my really high TDS. I shall experiment more with this...

Is there a gallon meter I can buy to monitor the amount of water I run through the RO/DI setup?

WOW, that does sound like a lot of chlorine. That would make sense as your source for the TDS in the tank and even more so if you also have chlorimines (spelling ?) in your water. If you had added water to the tank that was 0 TDS, I could very well believe that any grime or salt residue would certainly raise the TDS count up, but not that much.

If you can find it, try adding catalytic activated carbon when you need to replace your current ones. This stuff is said to be a lot better than regular activated carbon and I have noticed that my membrane and DI did last a little longer once I switched to it.

I have not sean any gauges like you have mentioned for a RO unit before, but I'm sure there must be one out there.

If you take your time to do the research FIRST, you can successfully set-up and keep ANY type of aquarium with ease."Not using a quarantine tank is like playing Russian roulette. Nobody wins the game, some people just get to play longer than others." - Anthony CalfoFishless CycleCycling with FishMarine Aquarium Info [URL="http://saltwater.aquaticcommunity.com/"]

Think using higher TDS wate could account for my random PH test's? I have a salifert and two hagen test kits. Both hagen test kits read 8.6-8.7ph while my salifert says 8.1? This is on the tank already running with the eel.

However, on the newly filled tank the 3 test kits read the same.. around 7 something.